Omnidirectional beacon antenna



Aug. 28, 1962 c. LUCANERA 3,051,951

OMNIDIRECTIONAL BEACON ANTENNA Filed Sept. 11, 1957 In ventorCOA/SMn/r/A/o UCM/ERA Attorney United States Patent O rind sept. 11,1957, ser. No. 683,917 s claims. (ci. 343-106) This invention relates toomnidirectional beacon antennas and more particularly to omnidirectionalbeacon antennas for use in producing a multilobed radiationpatternhaving -a fundamental modulation frequency and one or more additionalharmonics of the fundamental frequency for use in radio navigationsystems such as that commonly known as TACAN.

Omnidirectional beacon systems such as in TACAN have a high order ofdirectional @accuracy which is dependent upon the use of a directiveantenna pattern rotated at a fundamental frequency and modulated by aharmonic of fundamental frequency so `as to produce a generallymultilobed rotating ldirective radiation pattern. The antennas usuallyconsist of a central omnidirectional radiator surrounded by pat-ternmodifying elements .adapted to revolve around the .central radiator. Dueto the rotation of the multiple-modulation antenna pattern, a receiverlocated remotely from the .transmitter receives energy which appears rasan amplitudesmodulated wave `having a fundamental modulation componentand a modulation component at a harmonic frequency of the fundamental.Both fundamental and harmonic Ifrequency reference signals aretransmitted for comparison with the received components of the rotatingpattern so that the receiver may determine its azimuth relative to thebeacons lantenna. system.

In beacon systems of this type it is desirable to have the antennalsystem produce a vertical radiation pattern which provides goodcoverage at angles above lthe `horizon while having low radiation belowthe horizon to minimize site errors. Various arrangements have been usedto obtain the desired result. `One arrangement uses a central radiatorcomprising a vertical stack of elements such as cones. However, thisarrangement adds considerable height to the antenna Isystem 'and hassome additional disadvantages such as producing severe nulls in thepattern at certain vertical angles. Another disadvantage of previousantennas is that they provide coverage over -a relatively narrow band offrequencies.

The principal object of invention is to provide ian improved antenna fora beacon sys-tem having good vertical coverage over ya broad band o-ffrequencies.

Another 'object is to prov-ide such an yantenna system having a smallvertical height.

According .to one aspect of the invention, a beacon antenna system isprovided having the gener-al characteristics of a horn antennacomprising a rst conductive member having a generally horizontal atcounterpoise surface, and a .second conductive dish-shaped member whichis symmetrical about an axis extending perpendicular to lchecounterpoise surface `at the center thereof. rFhe second member isdisposed above the rst member with the closest spacing along the axis. Avertically polarized omnidirectional central radiator, such as aquarter-wavelength stub, is placed between the two members along theaxis. The counterpoise surface carries the pattern-modulating elementsand is rotated about the central radiator.

A further feature of the invention resides in providing the first memberwith .a second horizontal conductive sur-V face in a plane an oddnumber, such `as three, of quarter wavelengths below the counterpoisesurface to form a radio frequency (R.F.) choke which reduces radiationat negative vertical angles, that is, below the horizon.

3,951,951 Patented Aug. 28, 1952 ICC According to another aspect of theinvention, an R.F. choke in the form of an inverted cup having aquarterwavelength llange is placed -about the central feed line to 'thequarter-wavelength stub, the upper surface of the choke being Ian oddnumber of quarter wavelengths, such as three quarter wavelengths, belowthe feed point of the central radiator. IA quarter-wavelength hollowconductive sleeve may be placed Iaround the central radiator and feedline, symmetrical of the feed point.

The foregoing and other objects `and features of this invention and themanner of attaining them will become more apparent' and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings comprising FIGS. l and 2, wherein: l

FIG. l is a plan View of a beacon antenna system; and

FIG. 2 is a cross-section View, partly diagrammatic, taken `along lines2 2 of FIG. l.

Referring to the drawing, the disclosed embodiment of the antenna`system includes a conductive counter-poise surface 1 and a cone-shapedconductive member 2 disposed above the counterpoise surface with itsapex at its lower point along the axis perpendicular to the center ofthe counterpoise surface. A stationary central radiator comprising aquarter-wavelength stub 3 is placed between the counterpoise and theconical member and is vertically disposed along the axis. The centralradiator is fed by a transmission line 4, which consists of a length ofilexible coaxial cable 5 with the copper sheath removed and enclosed ina 34E-inch rigid hollow tubular conductor 6 which supports it. Thisforms a characteristic impedance of 50 ohms. The central coductor 7 ofthis transmission -li-ne is connected to 'a feed point :at the lower endof the stub radiator 3. The transmission line 4 is coupled to a sourceof R.F. energy, not shown.

To reduce the R.F. current owing on the outside of Ithe transmissionline and to prevent it from acting as a radiator, an R.F. choke in theform of an inverted cup 8 is placed around the transmission lineapproximately three quarter wavelengths from the feed point to the stub3. The flange 9 of the choke is approximately one quarter wavelengthlong. 'Ilhe cup Sis connected to the outer con- .ductos` 6 of thetransmission line 4. A length of hollow conductive tubing 1t) onequarter wavelength long is placed `around the stub 3 and transmissionline 4, symmetrically and concentrically in respect to the feed point,4t-o further 'aid in reducing the R.F. current on the line 4. Thissleeve 10 is supported by an insulating tube 11.

The central stationary elements includ-ing the radiator 3, transmissionline 4, inverted cup `8, and sleeve 10` are enclosed within a dielectriccylinder 12.

The rotating elements, including the counterpoise surface 1, aresupported by a dielectric cylinder 13, which is rotated at l5 lcyclesper second by an arrangement shown diagrammatically by a motor 14 and agear arrangement 1S.

To reduce the radiation at negative angles below the horizon and improvethe vertical pattern, a second horizontal conductive surface 16 isplaced three quarter wavelengths below the counterpoise surface 1. Thesurface 16 and the counter-poise surface 1 are electrically connected attheir inner edges by a tubular conductive cylindrical portion 17, whichis attached to the dielectric cylinder 13.

To provide the multilobed horizontal pattern, a parasitic element 18 isattached to cylinder 13 to provide a fundamental modulation, and nineparasitic elements 19 are equally spaced around the outer edge of thecounter' poise surface 1 to provide the ninth-harmonic modulation.

length long and insulated from counterpoise surface 1. However, ifdesired, they may be a quarter wavelength long and electricallyconnected to the counterpoise surface y1. A description of TACANantennas and the design considerations involved in determining thecharacteristics and location of the parasitic elements may be found inElectrical Communications, published by International Telephone andTelegraph Corporation, New York, New York, vol. 33, No. 1, March, 1956,pages 35-59. It has been found that one satisfactory type of parasiticelements may comprise 3z-inch hollow aluminum tubing. In somearrangements it may be desirable to slant the outer parasitic elementstoward the center and support them by means of insulators attached tocone 2. With such arrangement it would be necessary to rotate the cone 2and, therefore, it may be supported by the rotating dielectric cylinder13 as shown. However, with the parasitic elements vertically disposed asshown, the cone 2 should preferably be supported by the stationarydielectric cylinder 12 to reduce the weight of the rotating structure.

An antenna system comprising the above described new combination ofelements produces a `carrier radiation pattern which is omnidirectionalin the horizontal plane, and in vertical planes has a relatively highstrength from the horizon up to positive vertical angles of about 50,while having a relatively low strength at angles below the horizon. Thiscombination does not produce any appreciable nulls in the verticalpattern within the useful range, such as are characteristic of otherarrays.

The rotating parasitic modulating elements 18 and 19 produce a spacemodulation of the carrier pattern in the horizontal planes to giveazimuth bearing information. The arrangement according to this inventionproduces useful modulation from the horizon up .to fairly high verticalangles.

In a specific embodiment of the invention for use in the band of 960 to`1025 megacycles, the vertical spacing between the outer edge of cone 2and surface 1 is 12 inches, surface 16 is 10 inches below surface 1, theupper surface of the inverted cup 8 is 7 inches below the lower edge ofthe sleeve 10 and `61/4 inches below surface 1, the inner dielectriccylinder 12 has a diameter of 4 inches and the outer dielectric cylinder13 has a diameter of 51A; inches. The surfaces 1 and 16 have a diameterof 41 inches, and the dimension of the cone from the apex to the outeredge is ll inches.

While for optimum performance it is desirable that the combinationinclude all of the elements as described, satisfactory performance forsome purposes may be obtained with various subcombinations and these areconsidered as being within the scope of the invention.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

I claim:

l. An omnirange beacon antenna comprising a first conductive planarcounterpoise member, a conductive conical member disposed coaxiallyabout a common axis of said antenna and above said rst member with theapex of said conical member directed toward said first member, avertically polarized central radiator disposed along said axis andlocated between said counterpoise member and said conical member,dielectric supporting means connected to both said members and mountedfor rotation about said common axis, a transmission line disposed alongsaid common axis and connected to said central radiator, a plurality ofparasitic elements mounted on said rst member and disposed parallel tosaid axis, means to rotate said supporting means about said axis tocause said parasitic elements to rotate about said axis whereby therotation of said parasitic elements about said central radiator producesa multilobed rotating antenna pattern.

2. An omnirange beacon antenna comprising a iirst conductive planarcounterpoise member, a conductive conical mem-ber disposed coaxiallywith said counterpoise member about a common axis of said antenna andabove said counterpoise member with the apex of said conical memberdirected toward said counterpoise member, a vertically polarized centralradiator disposed along said axis and located between said counterpoisemember and said conical member and spaced apart from the apex of saidconical member, a second conductive planar counterpoise member disposedabout said common axis and located on the opposite side of said lfirstcounterpoise member from said lcentral radiator, dielectric supportingmeans -connected to said first and second counterpoise members and saidconical member and mounted for rotation about said common axis, aplurality of parasitic elements insulated from and mounted on said iirstcounterpoise member and disposed parallel to said axis, means to rotatesaid dielectric supporting means about said axis to cause said parasiticelements to rotate about said axis whereby the rotation of saidparasitic elements produces a multilobed rotating antenna pattern.

3. An omnirange beacon antenna comprising a rst conductive planarcounterpoise member disposed about a common axis of said antenna, asecond conductive planar counterpoise mem-ber disposed about said axisand spaced apart along said axis from said first counterpoise member, aconductive conical member disposed about said axis on the opposite sideof said second counterpoise member from said iirst counterpoise memberwith the apex of said conical member directed toward said secondcounterpoise member, a vertically polarized central radiatior disposedalong said axis between said second counterpoise member and said conicalmember and spaced apart from said conical member and said secondcounterpoise mem-ber, dielectric supporting means connected to both saidcounterpoise member and said conical member and mounted for rotationabout said axis and said central radiator, a plurality of conductiveparasitic elements disposed on said second counterpoise member on thesame side of said second counterpoise member as said central radiatorand disposed parallel to said axis, means to rotate said dielectricsupport means whereby the rotation of said parasitic elements about saidcentral radiator creates a multilobed rotating antenna pattern havingconsiderably greater radiation strength at points located on the sameside of said axis as said conical member as compared to points locatedon the opposite side of said axis.

4. An omnirange beacon antenna according to claim 3 wherein each of saidparasitic elements is one-quarter wavelength long and is electricallconnected to said counterpoise member.

5. An omnirange beacon antenna for producing a rotating multilobedantenna pattern comprising a first conductive planar counterpoise memberdisposed about a common axis of said antenna, a second conductive planarcounterpoise member disposed substantially parallel to said rst surfaceand spaced apart from said first member along said common axis, aconductive conical member disposed about said axis on the opposite sideof said second counterpoise member from said iirst counterpoise memberwith the `apex of said conical member directed toward said secondcounterpoise member, a vertically polarized central radiator disposedalong said axis between said second counterpoise member and said conicalmember and spaced apart therefrom, a fundamental parasitic elementinsulated from and mounted on said second counterpoise member anddisposed parallel to said axis and between said conical member and saidsecond counterpoise member, a plurality of parasitic elements insulatedfrom and mounted on ysaid second counterpoise member on the oppositeside of said member from said first counterpoise member and disposedparallel to said axis, dielectric support means connected to both saidcounterpoise members and said conical member and mounted for rotationabout said axis, means to rotate said support means connected to saidsupport means whereby the rotation of said parasitic elements about saidcentral radiator creates a rotating multilobed antenna pattern.

6. An omnirange beacon 'antenna -for producing a rotating multilobedantenna pattern comprising a first conductive planar counterpoise memberdisposed about a common axis of said antenna, a second conductive planarcounterpoise member disposed about said axis and spaced apart along saidaxis from said iirst counterpoise member, a conductive conical memberdisposed -about said axis on the opposite side of said secondcounterpoise member from said first counterpoise member with the apex ofsaid conical member directed toward said second counterpoise member, avertically polarized central radiator disposed along said axis betweensaid conical member and said second counterpoise member and spaced apartfrom both, dielectric support means connected to both said counterpoisemembers and said conical member and disposed for rotation about saidcommon axis, a fundamental parasitic element one-half wavelength longinsulated from and mounted on said second counterpoise member anddisposed parallel to said common axis and located between said conicalmember and said second counterpoise member, a plurality of harmonicparasitic elements one-half wavelength long insu-lated from and mountedon said conical member and said second counterpoise member, saidparasitic members being disposed along lines directed toward said commonaxis, means to rotate connected to said dielectric support means wherebythe rotation of said parasitic elements about said central radiatorproduces a rotating multilobed antenna pattern.

7. An omnirange beacon antenna for producing a rotating multilobedantenna pattern comprising a first conductive planar counterpoise memberdisposed about a common axis of said antenna, a second conductive planarcounterpoise member disposed substantially parallel to said rst memberand spaced apart therefrom along said axis, a conductive conical memberdisposed about said axis on the opposite side of said second member fromsaid irst member with the apex of said conical member directed towardsaid `second counterpoise member, a vertically polarized centralradiator disposed along said axis between said conical member and saidsecond counterpoise member and spaced apart from both said conicalmember and said second counterpoise member, a stationary transmissionline disposed along said axis and connected to said central radiator, aradio frequency choke mounted on said transmission line and disposedalong said -axis between said first and second counterpoise members, afundamental conductive parasitic element one-half wavelength longinsulated from and mounted on said second counter-poise member anddisposed between said conical member and said second counterpoisemember, a plurality of conductive parasitic elements insulated from andmounted on said second counterpoise member and disposed parallel to saidcommon axis and located at radii larger than the radius of the base ofsaid conical member, dielectric support means connected to both saidcounterpoise members and said conical member and mounted for rotationabout said common axis, drive means connected to said dielectric supportmeans to rotate said parasitic elements about said central radiatorwhereby the rotation of said parasitic elements creates a rotatingmultilobed antenna pattern.

8. An omnirange beacon antenna for producing a rotating multilobed-antenna pattern comprising a first conductive planar counterpoisemember disposed about a common axis of said antenna, a second conductiveplanar counterpoise member disposed substantially parallel to said iirstmember and spaced apart therefrom an odd number of half Wavelength alongsaid axis, a conductive conical member disposed about said axis on theopposite side of said second member from said tir-st member with theapex of said conical member directed toward Said second counterpoisemember, a vertically polarized central radiator disposed along said axisbetween said conical member and said second counterpoise member andspaced apart from both said conical member and both said counterpoisemembers, a stationary transmission line disposed along said axis andconnected to said central radiator and spaced apart from both saidcounterpoise members, a radio `frequency choke mounted on saidtransmission line and disposed along said axis between said rst andsecond counterpoise members, a fundamental conductive parasitic elementone-half Wavelength long insulated from and mounted on said secondcounterpoise member and disposed between said conical member and saidsecond counterpoise member at a first radius from said axis, a pluralityof harmonic conductive parasitic elements one-half wavelength longinsulated from and mounted on said second counterpoise member anddisposed parallel to said common axis and located at radii larger thanthe radius of the base of said conical member, said conical memberhaving a base whose radius is greater than said first radius of saidfundamental parasitic element, dielectric support means connected toboth said counterpoise members and said conical member 4and mounted forrotation about said common axis, drive means connected to saiddielectric support means to rotate and parasitic elements about saidcentral radiator whereby the rotation of said parasitic elements createsa rotating multilobed antenna pattern.

References Cited in the iile of this patent UNITED STATES PATENTS2,565,506 Litchford Aug. 28, 1951 2,928,087 Parker Mar. 8, 1960 FOREIGNPATENTS 495,977 Great Britain Nov. 23, 1938 114,368 Australia Dec. 9,1941

